In the last 30 days

• Open/close Diffraction in high numerical aperture systems: polarization effects

  L Ciocci et al  2010 J. Opt. 12 015408 Tag this article

  Article References Full text PDF (624 KB)

  In high numerical aperture systems polarization effects should be taken into account; hence it is necessary to use a vectorial diffraction theory to describe them. We develop a computational model to study image formation in a high numerical aperture microscope objective by simulating images of self-luminous, non-polarized point objects. We compare the predictions made by scalar and vectorial theories of diffraction. In the last case we also consider an analyzer placed behind the objective to study the polarization effects. We find that vectorial theory predicts a larger diffraction pattern and, when an analyzer is used, an enlargement along the transmission axis of the analyzer. We also study the resolution of the system, finding that the true resolution predicted for vectorial theory is approximately 10% lower than that usually expected for scalar theory.

• Open/close Few-optical-cycle pulses tunable from the visible to the mid-infrared by optical parametric amplifiers

  D Brida et al  2010 J. Opt. 12 013001 Tag this article

  Article References Full text PDF (1.79 MB)

  Ultrafast optical parametric amplifiers (OPAs) can provide, under suitable conditions, ultra-broad gain bandwidths and can thus be used as effective tools for the generation of widely tunable few-optical-cycle light pulses. In this paper we review recent work on the development of ultra-broadband OPAs and experimentally demonstrate pulses with durations approaching the single-cycle limit and almost continuous tunability from the visible to the mid-IR.

• Open/close A selectively coated photonic crystal fiber based surface plasmon resonance sensor

  Xia Yu et al  2010 J. Opt. 12 015005 Tag this article

  Article References Full text PDF (378 KB)

  We propose a novel design for a photonic crystal fiber based surface plasmonic resonance sensor. The sensor consists of selectively metal-coated air holes containing analyte channels, which enhance the phase matching between the plasmonic mode and the core-guided mode. Good refractive index sensitivity as high as 5500 nm/RIU (refractive index unit) can be achieved in the proposed structure. Compared with the entirely coated structure, the selectively coated sensor design demonstrates narrower resonance spectral width. Moreover, the greater resonance depth can improve the sensing performance in terms of signal to noise ratio (SNR). The improvements in spectral width and SNR can both contribute to a better detection limit for this refractive index sensor.

• Open/close The spaser as a nanoscale quantum generator and ultrafast amplifier

  Mark I Stockman  2010 J. Opt. 12 024004 Tag this article

  Article References Full text PDF (743 KB)

  Nanoplasmonics has recently experienced explosive development with many novel ideas and dramatic achievements in both fundamentals and applications. The spaser has been predicted and observed experimentally as an active element—a generator of coherent local fields. Even greater progress will be achieved if the spaser can function as an ultrafast nanoamplifier—an optical counterpart of the MOSFET (metal–oxide–semiconductor field effect transistor). A formidable problem with this is that the spaser has inherent feedback, causing quantum generation of nanolocalized surface plasmons and saturation and consequent elimination of the net gain, making it unsuitable for amplification. We have overcome this inherent problem and shown that the spaser can perform functions of an ultrafast nanoamplifier in two modes: transient and bistable. On the basis of quantum density matrix (optical Bloch) equations we have shown that the spaser amplifies with gain with a switching time  fs (potentially, ~10 fs). This prospective spaser technology will further broaden both fundamental and applied horizons of nanoscience, in particular enabling ultrafast microprocessors working at 10–100 THz clock speed. Other prospective applications are in ultrasensing, ultradense and ultrafast information storage, and biomedicine. The spasers are based on metals and, in contrast to semiconductors, are highly resistive to ionizing radiation, high temperatures, microwave radiation, and other adverse environments.

• Open/close Tunability parameters in SNOM tip mediated tuning of an ultra-high quality heterostructure resonator

  Sushil Mujumdar  2010 J. Opt. 12 035001 Tag this article

  Article References Full text PDF (485 KB)

  We study numerically the phenomenon of externally tuning the resonance of a photonic crystal multistep heterostructure with an ultra-high quality factor, using 3D finite difference time domain simulations. We exploit the system-specific parameters, namely the lattice constant offset and barrier width, offered by the unique architecture of a multistep heterostructure. Coupled with generic parameters, such as interaction volume and tip–sample spacing, we demonstrate that the tip-heterostructure system yields a powerful tunable device in photonic applications. We show how the fixed parameters can be used to assign the dynamic range and resolution of tunability, whilst the vertical motion of the tip realizes real-time, reversible, high fidelity tuning.

• Open/close Studies of random laser action in π-conjugated polymers

  A Tulek and Z V Vardeny  2010 J. Opt. 12 024008 Tag this article

  Article References Full text PDF (1.59 MB)

  Laser action usually occurs within carefully configured resonant cavities. However, stimulated emission in disordered systems may also lead to coherent laser action above a certain threshold excitation intensity, I _th, which was dubbed as 'random lasing'. In random lasing a sequence of spectrally narrow emission lines, which are characteristic of laser modes, is superimposed on the amplified spontaneous emission band. We studied the statistical threshold distribution function, F( I _th) of I _th, of random lasers in π-conjugated polymer films and its evolution with respect to the excitation area. The measurements were supported by pictures of the excited area taken while lasing occurs. We found that random lasing is accompanied by the appearance of lasing random cavities in the pictures, indicating that the sharp lines in the emission spectrum are, in fact, laser modes related to the random cavities formed in the disordered gain medium. Moreover a correlation exists between the cavity size extracted from the Fourier transform of the random lasing emission spectra and the size of the random resonators in the pictures obtained. In addition we also found that the measured F( I _th) has a marked asymmetry with respect to the average threshold, ( I _th) _ave, which decreases with the excitation area. An existing theoretical model based on random resonators in the polymer film is found to be in good agreement with the obtained F( I _th) function.

• Open/close Colloidal Au-enhanced surface plasmon resonance imaging: application in a DNA hybridization process

  M G Manera et al  2010 J. Opt. 12 035003 Tag this article

  Article References Full text PDF (1.23 MB)

  The detection of the DNA hybridization mechanism using monodispersed gold nanoparticles as labels is an interesting alternative to increase the sensitivity of the SPR imaging technique. DNA-modified Au nanoparticles (DNA-Au NPs) containing single-stranded (ss) portions of DNA were prepared by monitoring their monolayer formation by UV–vis spectroscopy. The hybridization process between specific thio-oligonucleotides immobilized on the DNA–Au NPs and the corresponding complementary strands is reported and compared with the traditional hybridization process on properly self-assembled thin gold films deposited on glass substrates. A remarkable signal amplification is observed, following the incorporation of colloidal Au into a SPR biosensing experiment, resulting in an increased SPR response to DNA–DNA interactions. In particular Fusarium thiolated DNA (5'HS poly(T) ₁₅ATC CCT CAA AAA CTG CCG CT-3) and trichothecenes complementary DNA (5'-AGC GGC AGT TTT TGA GGG AT-3') sequences have been explored due to their possible application to agro-industry for the control of food quality.

• Open/close Theory of extraordinary light transmission through sub-wavelength circular hole arrays

  Meng Zhang et al  2010 J. Opt. 12 015004 Tag this article

  Article References Full text PDF (265 KB)

  The light transmission through a square array of circular holes in a metal film has been studied theoretically, taking into account the diffraction modes and the surface plasmons. The calculations are in good agreement with experimental results. By studying the dependence of the transmission spectrum on the structural parameters of the hole array, we show that the transmission peaks are strongly correlated with the waveguide modes inside the cylindrical holes. Associated with the propagation characteristics (propagating or evanescent) of the waveguide modes, Fabry–Perot resonance in the circular holes or extended surface resonance on the metal films would give rise to the transmission peaks.

• Open/close Lasing in metamaterial nanostructures

  Anan Fang et al  2010 J. Opt. 12 024013 Tag this article

  Article References Full text PDF (1000 KB)

  A self-consistent computational scheme is presented for one-dimensional (1D) and two-dimensional (2D) metamaterial systems with gain incorporated into the nanostructures. The gain is described by a generic four-level system. The loss compensation and the lasing behavior of the metamaterial system with gain are studied. A critical pumping rate exists for compensating the losses of the metamaterial. There exists a wide range of input signals where the composite system behaves linearly. Nonlinearities arise for stronger signals due to gain depletion. The retrieved effective parameters are presented for one layer of gain embedded in two layers of Lorentz dielectric rods and split ring resonators (SRR) with two different gain inclusions: (1) gain is embedded in the gaps only and (2) gain is surrounding the SRR. When the pumping rate increases, there is a critical pumping rate at which the metamaterial system starts lasing.

• Open/close Recent developments in the theory of multimode random lasers

  Oleg Zaitsev and Lev Deych  2010 J. Opt. 12 024001 Tag this article

  Article References Full text PDF (332 KB)

  We review recent extensions of semiclassical multimode laser theory to open systems with overlapping resonances and inhomogeneous refractive index. An essential ingredient of the theory is a system of biorthogonal quasimodes that describe field decay in an open passive system and are used as a basis for lasing modes. We discuss applications of the semiclassical theory, as well as other experimental and numerical results related to random lasing with mode competition.